update essence API header

core/os/os_essence.odin

@@ -50,3 +50,6 @@ write :: proc(fd: Handle, data: []u8) -> (int, Errno) {
 	return (int) (0), (Errno) (1);
 }
 
+seek :: proc(fd: Handle, offset: i64, whence: int) -> (i64, Errno) {
+	return (i64) (0), (Errno) (1);
+}

core/time/time_essence.odin

@@ -1,2 +1,18 @@
 package time
-IS_SUPPORTED :: false;
+
+import "core:sys/es"
+
+IS_SUPPORTED :: true;
+
+now :: proc() -> Time {
+	// TODO Replace once there's a proper time API.
+	return Time{_nsec = i64(es.TimeStampMs() * 1e6)};
+}
+
+sleep :: proc(d: Duration) {
+	es.Sleep(u64(d/Millisecond));
+}
+
+_tick_now :: proc() -> Tick {
+	return Tick{_nsec = i64(es.TimeStampMs() * 1e6)};
+}